1. Field of the Invention
The present invention relates to a continuously variable transmission controller (hereinafter referred to as xe2x80x9cCVT controllerxe2x80x9d) capable of controlling a continuously-variable transmission (hereinafter abbreviated to xe2x80x9cCVTxe2x80x9d) for appropriate downshift operation while a vehicle mounted with the CVT is in an uphill traveling mode or in a downhill traveling mode.
2. Description of the Related Art
A conventional CVT controller for controlling a CVT determines a speed change ratio on the basis of throttle opening, and a parameter indicating an operating condition, such as a traveling speed or an engine speed, and determines a desired primary pulley speed by making reference to a basic speed change characteristic map, and varies the speed change ratio of the CVT continuously in the range of a low speed change ratio to an overdrive speed change ratio in a follow-up control mode so that actual primary pulley speed approaches the desired primary pulley speed.
In most cases, the basic speed change characteristic map is produced empirically on the basis of experimental results so that the vehicle loaded with a standard load is able to travel properly on a horizontal and flat road. Accordingly, if the speed change ratio is determined on the basis of such a basic speed change characteristic map, the torque of the driving system of the vehicle may be insufficient and the driver will feel an unpleasant feeling while the vehicle is in the uphill traveling mode, and an appropriate effect of engine brake is unavailable and the driver will feel unpleasant.
A technique disclosed in JP-A No. 6-81931 or 6-81932 subtracts running resistance including air resistance, acceleration resistance, rolling resistance and cornering resistance from the traction of an engine, calculates weight incline resistance during uphill traveling, determines a desired primary pulley speed correction corresponding to the weight incline resistance and a throttle opening by making reference to a map, adds the desired primary pulley speed correction to a desired primary pulley speed corresponding to the throttle opening and a traveling speed determined by making reference to a basic speed change characteristic map to correct the desired primary pulley speed.
If an estimated running resistance is excessively high and the traction is increased by an incremental traction corresponding to an excess running resistance over an expected running resistance, the CVT will be downshifted by an excessively large downshift amount and the engine speed will excessively be increased. A technique disclosed in JP-A No. 8-68448 decreases the rate of increase of an amount corresponding to a downshift amount (incline resistance, desired primary pulley speed) with the increase of incline resistance or throttle opening or sets an upper limit to the downshift amount to reduce an unpleasant sensation that may be felt by the driver.
However, if an incremental running resistance is compensated by downshift while the vehicle is traveling at a high traveling speed, downshift will increase engine speed greatly even if the incremental running resistance is small. Accordingly, the engine needs to operate at a high engine speed and noise and fuel consumption increase in a high traveling speed range. In a state where the vehicle is traveling at a small throttle opening, the output torque of the engine declines as engine speed increases, increase in traction exceeding a predetermined value cannot be expected from downshift and traction has a declining tendency, deceleration due to downshift will give an unpleasant feeling to the driver.
Accordingly, it is an object of the present invention to provide a CVT controller for controlling the shifting operation of a CVT, capable of properly determining a downshift amount by which the CVT is to be downshifted for the uphill or downhill traveling of a vehicle, of preventing excessive increase in engine speed, of suppressing increase in vibrations and noise, and of improving the maneuverability of the vehicle.
According to one aspect of the present invention, a CVT controller for controlling a CVT mounted on a vehicle comprises: an incremental running resistance setting means for setting an incremental running resistance based on a running resistance that will act on the vehicle when the vehicle is traveling in a flat road traveling mode on a horizontal, flat road according to traveling mode; a desired traction setting means for deciding whether the vehicle is in an uphill traveling mode or in a downhill traveling mode on the basis of the incremental running resistance, setting a desired traction for a full-open throttle state where a throttle valve is fully open on the basis of the incremental running resistance if the vehicle is in the uphill traveling mode and setting a desired traction for a fill-closed throttle state where the throttle valve is fully closed on the basis of the incremental running resistance if the vehicle is in the downhill traveling mode; a correction setting means for comparing the desired traction and an achieved traction in the full-open throttle state at a present traveling speed if the vehicle is in the uphill traveling mode, comparing the desired traction and an achieved traction in the fill-closed throttle state at a present traveling speed if the vehicle is in the downhill traveling mode, and determining a correction for adjusting the achieved traction to the desired traction; a speed change characteristic correcting means for correcting a basic speed change characteristic stored in a basic speed change characteristic map toward a downshift side; and a desired speed change ratio setting means for setting a desired speed on the basis of the corrected basic speed change characteristic.
The desired traction and an achieved traction in the full-open throttle state at a present traveling speed are compared if the vehicle is in the uphill traveling mode, the desired traction and an achieved traction in the full-closed throttle state at a present traveling speed are compared if the vehicle is in the downhill traveling mode, and a correction for adjusting the achieved traction to the desired traction is determined. A basic speed change characteristic stored in a basic speed change characteristic map is corrected toward a downshift side and a desired speed is set on the basis of the corrected basic speed change characteristic. Therefore, the speed change ratio can automatically be shifted by an appropriate amount of downshift according to the incremental running resistance based on the running resistance that may act on the vehicle while the vehicle is in the flat road traveling mode, the speed change ratio can properly be shifted toward the downshift side in the uphill traveling and the downhill traveling mode, excessive rise in engine speed due to inappropriate downshift can be avoided, and vibrations and noise can be suppressed. Since the speed change ratio is shifted toward the downshift side according to the increase of the incremental running resistance when the vehicle is in the uphill traveling mode, control input to the throttle valve (accelerator pedal) can be reduced. Since the speed change ratio is shifted toward the downshift side according to the reduction of the incremental running resistance when the vehicle is in the downhill traveling mode, operation necessary for using engine brake for downhill traveling can be simplified and hence the operation of the vehicle is improved greatly. Accordingly, the frequency of setting the engine for an accelerating mode during uphill traveling is reduced, and the frequency of fuel injection control operations for an accelerating mode can be reduced. Since the basic speed change characteristic is shifted toward the downshift side when the vehicle is in the downhill traveling mode to maintain the lowest speed change line on a high level to improve fuel consumption, a fuel cut region during downhill traveling can be expanded and, consequently, fuel consumption is improved. Since the lowest speed change line is held on a high level, the frequency of speed change ratio variation due to frequent operations for alternate stepping on and releasing the accelerator pedal (busy shift) can be reduced and the unpleasant sensation due to upshift resulting from the release of the accelerator pedal can be reduced.
In the CVT controller, the speed change characteristic correcting means may set a desired primary pulley speed for the flat road traveling mode by making reference to the basic speed change characteristic map and may correct the desired primary pulley speed by the correction toward a downshift side, and the desired speed change ratio setting means may set a desired speed on the basis of the corrected desired primary pulley speed. Thus, a desired primary pulley speed is set on the basis of the traveling mode for the flat road traveling mode by making reference to the basic speed change characteristic map, the desired primary pulley speed is corrected by the correction toward a downshift side to correct the speed change characteristic, a desired speed is set on the basis of the corrected desired primary pulley speed, and the present invention can readily applied to the conventional CVT controller.
The CVT controller may further comprise a correction coefficient setting means for setting a correction coefficient for the weighted correction of the incremental running resistance on the basis of traveling speed to reduce the incremental running resistance according to the increase of traveling speed when a present traveling speed is in a range not lower than a predetermined traveling speed, and the desired traction setting means may set the desired traction on the basis of a corrected incremental running resistance determined by correcting the incremental running resistance by using the correction coefficient. A correction coefficient is set for the weighted correction of the incremental running resistance on the basis of traveling speed to reduce the incremental running resistance according to the increase of traveling speed when a present traveling speed is in a range not lower than a predetermined traveling speed. The desired traction is set on the basis of a corrected incremental running resistance determined by correcting the incremental running resistance by using the correction coefficient. Therefore, the amount of downshift can be reduced, excessive rise in engine speed can be suppressed, vibrations and noise can be reduced and fuel consumption can be improved while the vehicle is traveling at traveling speeds in a high traveling speed range.
The CVT controller may further comprise a correction coefficient setting means for setting a correction coefficient for the weighted correction of the incremental running resistance on the basis of traveling speed to reduce the incremental running resistance according to the increase of traveling speed when a present traveling speed is in a range not lower than a predetermined traveling speed, the correction setting means may correct the correction by using the correction coefficient, and the speed change characteristic correcting means may correct the basic speed change characteristic stored in the basic speed change characteristic map by using the corrected correction toward a downshift side. A correction coefficient is set for the weighted correction of the incremental running resistance on the basis of traveling speed to reduce the incremental running resistance according to the increase of traveling speed when a present traveling speed is in a range not lower than a predetermined traveling speed. The correction is corrected by using the correction coefficient, and the basic speed change characteristic stored in the basic speed change characteristic map is corrected by using the corrected correction toward a downshift side. Therefore, the amount of downshift can be reduced, excessive rise in engine speed can be suppressed, vibrations and noise can be reduced and fuel consumption can be improved while the vehicle is traveling at traveling speeds in a high traveling speed range.
The CVT controller may further comprise a correction coefficient setting means for setting a correction coefficient for the weighted correction of the incremental running resistance on the basis of traveling speed to reduce the incremental running resistance according to the increase of traveling speed when a present traveling speed is in a range not lower than a predetermined traveling speed, the correction setting means may correct the correction by using the correction coefficient to provide a corrected correction, and the speed change characteristic correcting means may correct the desired primary pulley speed for the flat road traveling mode set by making reference to the basic speed change characteristic map on the basis of a traveling mode toward a downshift side by using the corrected correction. A correction coefficient is set for the weighted correction of the desired primary pulley speed on the basis of traveling speed to reduce the desired primary pulley speed according to the increase of traveling speed when a present traveling speed is in a range not lower than a predetermined traveling speed. The correction is corrected by using the correction coefficient to provide a corrected correction. The desired primary pulley speed for flat road traveling set by making reference to the basic speed change characteristic map on the basis of a traveling mode is corrected toward a downshift side by using the corrected correction. Therefore, the amount of downshift can be reduced, excessive rise in engine speed can be suppressed, vibrations and noise can be reduced and fuel consumption can be improved while the vehicle is traveling at traveling speeds in a high traveling speed range.
In the CVT controller, the incremental running resistance setting means may stop an operation for setting the incremental running resistance if brakes are being applied and may hold an incremental running resistance set in the preceding incremental running resistance setting cycle. An operation for setting the incremental running resistance is stopped if brakes are being applied and an incremental running resistance set in the preceding incremental running resistance setting cycle is held. Therefore, the introduction of errors in the calculated incremental running resistance due to the influence of deceleration can be prevented, and the incremental running resistance can accurately be calculated to enhance the reliability of the downshift correction of the speed change ratio.
In the CVT controller, the correction coefficient setting means may set the correction when the vehicle is traveling at a traveling speed in a traveling speed range excluding very low traveling speeds and high traveling speeds. The correction is set when the vehicle is traveling at a traveling speed in a traveling speed range excluding very low traveling speeds and high traveling speeds. Therefore, unnecessary operations for downshift correction in the very low traveling speed range and the high traveling speed range not requiring the downshift correction of the speed change ratio can be avoided.
In the CVT controller, the correction setting means may hold a correction set in the preceding correction setting cycle if an incremental traction increased after the downshift correction of traction is small as compared with the traction for uphill traveling. A correction set in the preceding correction setting cycle is held if an incremental traction increased after the downshift correction of traction is small as compared with the traction for uphill traveling to avoid unnecessary downshift. Therefore, the correction determined in the preceding cycle is held to avoid unnecessary downshift operations when increase in traction by increasing the amount of downshift while the vehicle is in the uphill traveling mode cannot be expected and hence an unpleasant sensation to the driver due to insufficient output power of the engine can be reduced.
In the CVT controller, the correction setting means may hold a correction set in the preceding correction setting cycle if a decremental traction decreased after the downshift correction of traction is small as compared with the traction for downhill traveling. A correction set in the preceding correction setting cycle is held if a decremental traction decreased after the downshift correction of traction is small as compared with the traction for downhill traveling to avoid unnecessary downshift. Therefore, the correction determined in the preceding cycle is held to avoid unnecessary downshift operations when increase in engine brake force by increasing the amount of downshift while the vehicle is in the downhill traveling mode cannot be expected and hence an unpleasant sensation to the driver due to insufficient engine brake force and such can be reduced.
In the CVT controller, the correction setting means may hold a correction set in the preceding correction setting cycle if the value of a parameter indicating load on the engine during uphill traveling is less than a predetermined value. It is decided that the driver has no intention of accelerating the vehicle if the value of a parameter indicating load on the engine during uphill traveling is less than a predetermined value, and a correction set in the preceding correction setting cycle is held. Therefore, unnecessary downshift operation when the driver has not intention of accelerating the vehicle while the vehicle is in the uphill traveling mode can be avoided to prevent giving an unpleasant sensation to the driver.
In the CVT controller, the correction setting means may hold a correction set in the preceding correction setting cycle if the value of a parameter indicating load on the engine during downhill traveling is not smaller than a predetermined value. It is decided that the driver has no intention of applying the brakes if the value of a parameter indicating load on the engine during downhill traveling is not smaller than a predetermined value, and a correction set in the preceding correction setting cycle is held. Therefore, unnecessary downshift operation when the driver has not intention of using engine brake while the vehicle is in the downhill traveling mode can be avoided to prevent giving an unpleasant sensation to the driver.